Magnetic imaging (MRI) is a technique which utilizes the nuclear magnetic resonance phenomenon (NMR) for finding out the nuclear density of an object and the local distributions of the NMR characteristics associated with a nucleus or the physical and chemical properties effecting them. Such NMR characteristics include e.g.: longitudinal relaxation (characterized by longitudinal relaxation time T1), transverse relaxation (characterized by transverse relaxation time T2), relaxation in a spinning set of coordinates (characterized by relaxation time T1rho), chemical shift, internuclear coupling factors. NMR characteristics are affected by physical phenomena, e.g.: flow, diffusion, paramagnetic materials, ferromagnetic materials, viscosity and temperature.
Techniques and applications of magnetic resonance and magnetic imaging have been described in a number of references: Stark DD and Bradley WG: Magnetic resonance imaging, C. V. Mosby Comp., St. Louis 1988, Gadian DG: Nuclear magnetic resonance and its applications to living systems, Oxford Univ. Press, London 1982, Shaw D: Fourier transform NMR spectroscopy, Elsevier, Amsterdam 1984, Battocletti JH: NMR proton imaging, CRC Crit. Rev. Biomed. Eng. vol. 11, pp. 313-356, 1984, Mansfield P and Morris PG: NMR imaging in biomedicine, Adv. in magnetic resonance, Academic Press, New York 1982, Abragam A: The principles of nuclear magnetism, Clarendon press, Oxford 1961, Lasker SE and Milvy P (eds.): Electron spin resonance and nuclear magnetic resonance in biology and medicine and magnetic resonance in biological systems, Annals of New York Academy of Sciences vol. 222, New York Academy of Sciences 1973, Sepponen RE: Discrimination and characterization of biological tissues with magnetic resonance imaging: A study on methods for T1, T2, T1rho and chemical shift imaging, Acta polytechnica scandinavica EL-56, Helsinki 1986, Fukushima E and Roeder SB: Experimental pulse NMR, Addison Wesley, London 1981, Anderson WA et al: U.S. Pat. No. 3 475 680, Ernst RR: U.S. Pat. No. 3 501 691, Tomlinson BL et al: U.S. Pat. No. 4 034 191, Ernst RR: U.S. Pat. No. 3 873 909, Ernst RR: U.S. Pat. No. 4 070 611, Bertrand RD et al: U.S. Pat. No. 4 345 207, Young IR: U.S. Pat. No. 4 563 647, Hofer DC et al: U.S. Pat. No. 4 110 681, Savolainen MK: Magnetic resonance imaging at 0.02 T: Design and evaluation of radio frequency coils with wave winding, Acta polytechnical scandinavica Ph 158, Helsinki 1988, Sepponen RE: U.S. Pat. No. 4 743 850, Sepponen RE: U.S. Pat. No. 4 654 595, Savolainen MK: U.S. Pat. No. 4 712 068, Sepponen RE: U.S. Pat. No. 4 587 493, Savolainen MK: U.S. Pat. No. 4 644 281 and Kupiainen J: U.S. Pat. No. 4 668 904. Dynamic nuclear polarization has been described e.g. in the following references: Lepley AR and Closs GL: Chemically induced magnetic polarization, Wiley, New York 1973, Potenza J: Measurement and Applications of dynamic nuclear polarization, Adv. Mol. Relaxation Processes vol 4, Elsevier, Amsterdam 1972, pp. 229-354, Ettinger KV: U.S. Pat. No. 4 719 425.
DNP is a magnetic double resonance technique which thus requires two separate spin populations. Such spin populations include e.g. the spins of electrons and protons. In the double resonance technique, the distribution of one spin population on various energy levels is altered and the other spin population is under observation. As certain conditions are fulfilled, the resonance signal of the spin population under observation grows. The amplitude of the amplified signal may be several hundred times greater than an unamplified signal. The amplification factor can be positive or negative. The amplified signal is characteristically highly sensitive to the physico-chemical properties and reactions of the spin environment, so its applicability to the examination of the chemical properties of a material is obvious.
The cited reference Ettinger KV: U.S. Pat. No. 4 719 425 discloses as applications the mapping of the contents of paramagnetic ingredients and the mapping of the activity of cerebral nerve cells.
The references Lurie DJ, Bussel DM, Bell LH, Mallard JR: Proton Electron Double Resonance Imaging: A new method for imaging free radicals, Proc. S.M.R.M. Fifth Annual Meeting, 1987, New York, p. 24 and Lurie DJ, Bussel DM, Bell LH, Mallard JR: Proton-Electron Double Magnetic Resonance Imaging of free radical solutions, J. Magn. Reson., vol. 76, 1988, pp. 366-370 disclose as possible applications the mappings of free radical groups, nitroxide radicals and the degree of oxidation.